The present invention pertains generally to loudspeakers, and more particularly to an improved system for aligning and supporting a magnetic assembly in a loudspeaker of the type which reciprocates a coil through an annular flux gap in response to a current through the coil.
A representative prior-art loudspeaker is described in U.S. Pat. No. 3,983,337, wherein an annular flux gap is formed in part by a metal loop which is both expensive to fabricate and undesirably bulky. A frame supports a forward end of the metal loop, which in turn cantilevers back therefrom to provide support for a magnet and center pole. An additional problem with a magnetic assembly of such construction is the difficulty in achieving proper alignment of the various parts, which is necessary for reliable sound reproduction.
Embodied in a more recent design, described in my co-pending application Ser. No. 669,315, now U.S. Pat. No. 4,115,667, are various improvements over the above-mentioned loudspeaker including, for example, a more compliant suspension system and lighter weight acoustic radiator assembly. Such improvements provide increased electromagnetic drive efficiency, which in turn permits the employment of a simplified, lighter weight magnetic assembly. Briefly, the magnetic assembly described therein comprises a toroidal shaped permanent magnet, adjoining toroidal shaped front and back pole plates, a cylindrical center post affixed to the back pole plate and extending forward through the magnet and front pole plate to provide an annular flux gap between the adjacent surfaces of the front pole plate and center post, and a frame mounted on the forward-most major surface of the front pole plate for supporting an acoustic radiator assembly including radiating surfaces and a voice coil.
In spite of the significant improvements over the prior-art loudspeaker, this more recent design still presents certain problems. In particular, alignment of the various component parts of the loudspeaker has proved difficult and time consuming. The use of a fast curing adhesive (cyanoacrylate) at the interfaces between the magnet and pole plates requires special alignment fixtures. Furthermore, in order to assure proper alignment of the acoustic radiator assembly with respect to both the frame and the magnetic assembly, special attention must be given to aligning the frame with respect to the front pole plate.